Storage tube for scan standards conversion



g- 1965 E. B. B. CALLICK ETAL 3,202,855

STORAGE TUBE FOR SCAN STANDARDS CONVERSION Filed June 16. 1961 \NVENTORS United States Patent Office 3,262,855 Patented Aug. 24, 1965 3,202,855 STORAGE TUBE FGR SCAN STANDARDS CQNVERSIGN Eric Brian Butler Caliick and Jervois Campbell Firmin, Chelmsford, Engiand, assignors to English Electric Valve Company Limited, London, England. a British company Filed June 16, 1 961, Ser. No. 117,598 Claims priority, application Great Britain, Aug. 29, 1969,

29,767/60 8 Claims. (Cl. 3 13-71) This invention relates to cathode ray tubes and has for its object to provide improved cathode ray tubes adapted to act as scan conversion tubes, i.e., adapted to provide from a set of input signals in accordance with one set of standards, a set of corresponding output signals in accordance with another set of standards. Although not limited to its application thereto, tubes in accordance with the invention are particularly useful for converting television signals in accordance with one set of television standards, i.e., a given number of lines per frame and a given number of frames per second into television signals in accordance with another set of television standards involving a different number of lines per frame and/or frames per second. The invention is, however, not limited to this type of application but may be used wherever scan conversion is required, e.g., for converting video signals in accordance with polar coordinate scanning (such as might be obtained from a radar system and be displayed, ordinarily, as a P.P,I. picture) into video signals in accordance with a television line raster suitable for display as a television picture. The invention seeks to provide scan conversion cathode ray tubes which will translate video signals in accordance with one set of standards into video sigals in accordance with another without producing a visible picture as an intermediate stage in the process of conversion; which will effect scan conversion without requiring the use of optical lenses or other expensive optical equipment; and which shall produce little (if any appreciable) reduction of signal-to-noise ratio in effecting scan conversion.

According to this invention a scan conversion cathode ray tube comprises within an evacuated envelope an insulating charge storing target mesh; a writing electron gun adapted to scan said target mesh with an electron beam modulated with signals in accordance with a given set of standards to store thereon charges corresponding to said signals; means for projecting a flood beam of electrons towards said target mesh to flood the same over substantially its whole area at substantially uniform ele'c- V tron density; a charge storing target electrode positioned to receive flood beam electrons which have passed through the target mesh; and a reading electron gun adapted to scan said target electrode in accordance with another given set of standards to develop output signals corresponding to the charge image produced on said target electrode by flood beam electrons which have passed through said target mesh.

In one embodiment of the invention a scan conversion tube comprises within an evacuated envelope a charge storing dielectric target mesh; a writing electron gun on one side of said mesh and adapted to scan said mesh in accordance with a given set of scanning standards with a signal modulated electron beam; a flood electron gun on said one side of said target mesh and adapted to flood it with an electron beam of substantially uniform density; a target electrode of the image orthicon cathode ray tube type positioned on the other side of said target mesh to receive, from flood gun electrons which have passed through the target mesh, an electrical charge image corresponding to that written on said target mesh by the writing gun; and, on the side of said target electrode remote from said target mesh, means, including a reading electron gun and an associated dynode system of the image orthicon cathode ray tube type, for scanning the target electrode in accordance with a second given set of scanning standards to develop output picture signals corresponding to the charge image on the target electrode.

The charge storing target mesh may be of any suitable type as commonly employed in signal displaying storage cathode ray tubes or it may be as described in the specification accompanying our co-pending application Serial No. 90,716, filed February 2, 1961. In any event there is preferably a grid or mesh provided adjacent the target mesh on the side thereof facing the target electrode. Also, instead of using an ordinary flood electron gun to flood the target mesh with electrons, the required substantially uniform density flood beam may be obtained from a large area cathode which may, in practice, extend over almost the whole of the operating cross section of the tube envelope.

In use the signal modulated beam from the writing gun is deflected in accordance with one set of standards and the reading gun is subjected to deflection in accordance with another set of standards. The necessary deflections may be accomplished in any convenient manners well known per se, i.e., electromagnetically by deflection coils or electrostatically by deflection plates, or deflection may be electromagnetic for either beam and electrostatic for the other. The writing beam writes a charge image on the target mesh. The flood beam floods the target mesh and electrons of this beam pass through to the target electrode in dependence on the charges on the target mesh. The target is scanned by the reading beam as in an image orthicon tube to produce output signals as in that well known type of tube.

The target mesh must, of course, have an appropriate decay time for stored charges and preferably means, as known per so, are provided for applying erasure pulses to a backing electrode forming part of a structure including said target mesh to control and adjust the decay time. In the case of converting television signals, the train of erasure pulses will normally be controlled by frame synchronising pulses in the incoming television signal wave form, though in some cases it may be preferred to control the erasure pulses by frame synchronising pulses in the output television signals.

The invention is illustrated in the drawings in which:

FIGURE 1 is a combined pictorial and schematic representation of one illustrative embodiment of this invention; and

FIGURE 2 is a combined pictorial and schematic representation of another illustrative embodiment of this invention.

Referring to FIG. 1, the scan conversion tube therein represented has at one end of its evacuated envelope an electron gun and associated secondary electron multipliers or dynodes, this gun and dynode unit being represented diagrammatically at 1 and being of a type commonly employed in image orthicon tubes; an electromagnetic focusing and deflecting coil assembly 2 outside the envelope; a so-cal'led field mesh 3; a target electrode 4, normally of glass and of a type commonly employed in image orthicon tubes; and, closely adjacent the target electrode 4, a collector mesh 5.

The tube parts so far described closely resemble the corresponding parts of an image orthicon tube. In place, however, of the normally provided photo-cathode section of an image orthicon tube, there are provided the further parts now to be described. These further parts include a dielectric target mesh 6 on the side of the collector mesh 5 remote from the target 4, the target mesh 6 being of a type commonly employed in signal display storage tubes; a collector mesh 7 associated with the target mesh 6; a writing gun 9 adapted to scan the target mesh 6; and a flood gun 8 adapted to flood the target mesh 6 with a substantially uniform density beam of electrons. As shown the flood gun 8 is co-axial and the writing gun 9 is offset a little. In use, incoming signals, e.g., television signals in accordance with a given set of standards, are applied in well known manner to a suitable electrode of the gun 9 to modulate the beam from this gun in accord ance with the signals, the frame and line scanning waveforms of which are applied to deflect the beam from the gun 9 to scan the target mesh 6. So as not to complicate the drawing the means for causing the beam from the gun 9 to scan the target mesh 6 are not shown but they may be electrostatic or electromagnetic and, of course, the normal focusing means (not shown) are also provided. In use, therefore, the gun 9 writes an electric charge image on the target mesh 6. The decay time of this image is controlled by the application of suitable pulses to the backing electrode (not separately shown) of the target mesh as in an ordinary signal display storage tube. In this way the persistence of the Written charge image can be made to suit requirements. Flood electrons from the flood gun 8 pass through the target mesh 6 and produce upon the target electrode 4 a charge image very like that which is produced on the target of an ordinary image orthicon tube by the photo cathode section of that tube. The charge image on the target electrode 4 is read off by the gun system 1 in exactly the same way as in an image orthicon tube, the reading beam from the gun It being deflected to scan the target electrode 4 in accordance with the scanning standards of the signals into which the input signals are to be converted. So as not to complicate the drawing, connections are shown only to the guns 8 and 9 and to the gun unit 1, the arrow heads representing the directions of input and output signals. In practice, of course, suitable external connections (not shown) are provided for enabling suitable operating potentials to be applied to the different electrodes of the tube.

The invention has the advantage that loss of signal-tonoise ratio due to conversion is quite small since the operation is entirely electronic and there is no intermediate stage of conversion of incoming signals into visible pictures with the use of photo-cathodes or luminescent screens. All the defects associated with luminescent screens, e.g., loss of definition by light scattering and halation and like optical effects, are avoided. Furthermore, there are no optical lenses or other expensive or fragile optical equipment necessary.

In operation the two sections of the tube-the writingstoring section and the reading section-are set up independently in accordance with well known principles. The potential between the collector mesh 5 and the backing electrode of the target mesh 6 is preferably adjustable and is adjusted to give the desired penetration of the flood beam through the target mesh 6. As already stated, the decay characteristic of the storage target mesh 6 is controlled by suitable erasure pulses applied to the backing electrode of this mesh and, in the case of television scan conversion, these erasure pulses may be controlled by frame synchronising pulses either (more usually) from the incoming television signals or from the outgoing television signals.

FIGURE 2 shows a modification which requires very little further description in view of the fact that like references are used for like parts in both figures. The principal differences between the arrangement of FIGURE 2 and that of FIGURE 1 is that in the latter figure the storage section of the tube is somewhat similar to that described in the specification accompanying our co-pending application Ser. No. 90,716, filed February 21, 1961, the target mesh structure including a grid close on each side of the mesh as in the illustrated embodiment of the said copending specification; the writing gun 9 is co-axial; the flood gun 8 of FIGURE 1 is replaced .by a large area cathode, here referenced 81, extending right across the envelope; and the whole of the storage section of the tube is immersed in a longitudinal magnetic field produced by a coil system 21 and similar to that used in the reading section of the tube, the writing beam being scanned over the target mesh 6 in a similar way to the reading beam in an image orthicon.

We claim:

1. A scan conversion cathode ray tube comprising with in an evacuated envelope an insulating charge storing target mesh; 21 writing electron gun adapted to scan said target mesh with an electron beam modulated with sig nals in accordance with a given set of standards to store thereon charges corresponding to said signals; means for projecting a flood beam of electrons towards said target mesh to flood the same over substantially its whole area at substantially uniform electron density; a charge storing target electrode positioned to receive flood beam electrons which have passed through the target mesh; and a reading electron gun adapted to scan said target electrode in accordance with another given set of standards to develop output signals corresponding to the charge image produced on said target electrode by flood beam electrons which having passed through said target mesh.

2. A scan conversion cathode ray tube comprising within an evacuated envelope a charge storing dielectric tar-get mesh; a writing electron gun on one side of said mesh and adapted to scan said mesh in accordance with a given set of scanning standards with a signal modulated electron beam; a flood electron gun on said one side of said target mesh and adapted to flood it with an electron beam of substantially uniform density; a target electrode of the image orthicon cathode ray tube type positioned on the other side of said target mesh to receive, from flood gun electrons which have passed through the target mesh, an electrical charge image corresponding to that written on said target mesh by the writing gun; and, on the side of said target electrode remote from said target mesh, means, including a reading electron gun and an associated dynode system of the image orthicon cathode ray tube type, for scanning the target electrode in accordance with a second given set of scanning standards to develop output picture signals corresponding to the charge image on the target electrode.

3. A tube as claimed in claim 1 wherein a grid is provided adjacent the target mesh on the side thereof towards the target electrode.

'4. A tube as claimed in claim 1 wherein the target mesh is between two grids, one on each side thereof and adjacent thereto.

5. A tube as claimed in claim 1 wherein the means for projecting the flood beam of electrons comprises a cathode having an area substantially the same as that of the target mesh and of the target electrode.

6. A tube as claimed in claim 2 wherein a grid is provided adjacent the target mesh on the side thereof towards the target electrode.

7. A tube as claimed in claim 2 wherein the target mesh is between two grids, one on each side thereof and adjacent thereto.

3. A tube as claimed in claim 2 wherein the flood electron gun includes a cathode having an area substantially the same as that of the target mesh and of the target electrode.

(References on fcilowing page) 5 6 References Cited by the Examiner 2,785,328 3/57 Kihn 313-68 2,864,031 12/58 Smith 31368X UNITED STATES PATENTS 2,918,600 12/59 'Pensak 313-68 X 2,280,191 4/42 Hergem'ot-her 315*12 X 2,532,339 12 5 Schlegingsr 315 12 5 GEORGE N-WESTBYPWMY Exammer- 2,687,492 4/54 Szegho et a1. 315-12 ARTHUR GAUSS, ROBERT SEGAL, Examiners. 

1. A SCAN CONVERSION CATHODE RAY TUBE COMPRISING WITHIN AN EVACUATED ENVELOPE AN INSULATING CHARGE STORING TARGET MESH; A "WRITING" ELECTRON GUN ADAPTED TO SCAN SAID TARGET MESH WITH AN ELECTRON BEAM MODULATED WITH SIGNALS IN ACCORDANCE WITH A GIVEN SET OF STANDARDS TO STORE THEREON CHARGES CORRESPONDING TO SAID SIGNALS; MEANS FOR PROJECTING A FLOOD BEAM OF ELECTRONS TOWARDS SAID TARGET MESH TO FLOOD THE SAME OVER SUBSTANTIALLY ITS WHOLE AREA AT SUBSTANTIALLY UNIFORM ELECTRON DENSITY; A CHARGE STORING TARGET ELECTRODE POSITIONED TO RECEIVE FLOOD BEAM ELECTRONS WHICH HAVE PASSED THROUGH THE TARGET MESH; AND A READING ELECTRON GUN ADAPTED TO SCAN SAID TARGET ELECTRODE IN ACCORDANCE WITH ANOTHER GIVEN SET OF STANDARDS TO DEVELOP OUTPUT SIGNALS CORRESPONDING TO THE CHARGE IMAGE PRODUCED ON SAID TARGET ELECTRODE BY FLOOD BEAM ELECTRONS WHICH HAVING PASSED THROUGH SAID TARGET MESH. 